fetch_and_save_url · Nav MCP: Risk & Policy

WHAT IT DOES

What fetch_and_save_url does on Navmcp

AI agents use fetch_and_save_url to create or update resources in Navmcp — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Navmcp environment.

WHY IT NEEDS A POLICY

Why fetch_and_save_url needs a policy

The name suggests two operations: fetching a URL (Read) and saving the result (Write). 'Save' implies writing data to disk or storage, which is the more severe of the two actions. Without a description, confidence is low, but the naming pattern on this server (alongside tools like 'download_pdfs' and 'convert_file_to_markdown') suggests it retrieves and persists content locally.

From the tool's definition Tool name 'fetch_and_save_url' — description is empty and uninformative.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

fetch_and_save_url Rate-limited

fetch_and_save_url stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "fetch_and_save_url": {
      "limits": [
        {
          "counter": "fetch_and_save_url_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Navmcp, so you can run agents against it safely.

FAQ

Questions about fetch_and_save_url

What does the fetch_and_save_url tool do? +

fetch_and_save_url. It is categorised as a Write tool in the Navmcp MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on fetch_and_save_url? +

Register the Nav MCP server in PolicyLayer and add a rule for fetch_and_save_url: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Navmcp. Nothing to install.

What risk level is fetch_and_save_url? +

fetch_and_save_url is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit fetch_and_save_url? +

Yes. Add a rate_limit block to the fetch_and_save_url rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block fetch_and_save_url completely? +

Set action: deny in the PolicyLayer policy for fetch_and_save_url. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides fetch_and_save_url? +

fetch_and_save_url is provided by the Nav MCP server (jianlins/navmcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.